The use of an exhaust gas recirculation, or EGR, system to recirculate exhaust gas from an internal combustion engine to an inlet air path of the engine is well known. By introducing recirculated exhaust gas, or EGR gas, to the inlet air path, the level of certain undesirable engine emission constituents such as oxides of nitrogen (NOx) can be reduced and fuel economy may improve. Up to a limit, NOx emissions decrease with increasing EGR gas levels. Beyond the limit, EGR gas can increase formation of other undesirable engine emission constituents and can reduce vehicle drivability.
Exhaust gas recirculation typically involves recirculation of exhaust gas through an EGR passage between an engine exhaust conduit, such as an exhaust manifold, and a fresh air intake passage, such as an intake manifold. A valve, often referred to as the EGR valve, is typically provided in communication with the EGR passage and is controllable to variably restrict the passage to regulate the flow of exhaust gas therethrough. When EGR gas is not required or desired, the EGR valve is driven to a full restriction (closed) position, typically through a spring preload. The spring preload is commonly required to be substantial, to ensure rapid closing of the EGR valve when necessary, and to ensure proper sealing of the closed EGR valve. When EGR gas is required, the EGR valve is driven to an open position through application of a position control signal to an actuator mechanically linked to the EGR valve. The degree of opening of the EGR valve varies with the magnitude of the position control signal.
With the EGR valve in the open position, EGR gas enters the intake manifold and flows to the engine cylinders. For optimum performance, the EGR gas should thoroughly mix with the inlet air so that each cylinder receives substantially identical proportions of EGR gas. Typically, the EGR gas is supplied to the intake air immediately prior to entering an intake manifold to minimize the response time between the EGR valve opening and EGR gas reaching the engine cylinders and to maximize EGR gas distribution.
Intake manifolds for use in automotive applications have traditionally been manufactured from metallic materials having high temperature durability, such as cast iron, alloys of aluminum, or magnesium. More recently, weight and manufacturing concerns have given rise to the use of thermoplastics on engines. When used in the construction of intake manifolds, weight may be reduced and, in many cases, performance may be improved as a result of precise control of interior finish and reduced heat transfer to the inlet air. Incorporation of the EGR system within thermoplastic intake manifolds is a principle design challenge since EGR gas is typically communicated to the intake manifold at high temperature.